A large number of color hardcopy images are being produced daily using a wide variety of image production processes such as conventional photography, lithography, xerography and inkjet printing. The images produced on these different media are often scanned subsequently, either for the purposes of copying or for creating an electronic representation for use in various applications. It is desirable that the scanning process accurately record the color information in the original hardcopy images. Since the spectral-response of typical scanners are not equivalent to those of a typical human observer, accurate color calibration can be obtained only if the correct medium dependent calibration is used for calibrating a color image. If the incorrect scanner color calibration is used, very significant color errors may be obtained. See for instance, “The Impact of UCR on Scanner Calibration, G. Sharma, S. Wang, D. Sidavanahalli, and K. Knox, Proc. IS&T's 1998 PICS conference, pp. 121-124.
In order to accurately calibrate a scanner, such as, for example, a color scanner, that scans an image carried on a substrate, different calibration transformations are required depending on the marking process, such as, for example, photography, inkjet printing, xerography, lithography and the like, and materials, such as, for example, toner, pigment, ink, etc., that are used to form the image on the substrate. For example, a calibration transformation that is used to calibrate the scanner for a photographic image is different from a calibration transformation that is used to calibrate the scanner for an ink jet-printed image, which is in turn different from a calibration transformation that is used to calibrate the scanner for a xerographically-formed image or for a lithographically-formed image. Additional accuracy may also be obtained in finer grain classification of the input image within each of these categories.
Typically, a user wishing to scan an image determines the marking process used to form the image from prior knowledge of the marking process, manually identifies the marking process such as, for example, photographic, ink jet, xerographic or lithographic, and uses the marking process information to set the scanner so that an appropriate calibration can be used. The manual identification is commonly done using different descriptions, such as Halftone vs. Photo vs. Xerographic Copy on the user interface from which different machine settings are inferred. Operator identification of the scanned medium can eliminate the problem of casts and color errors resulting from the use of an incorrect scanner calibration. However, this process is not only cumbersome but also correct identification of the input medium cannot be readily expected from novice users.
Previously, in D/A1366 an automatic method for identification of the medium without requiring additional information or operator input was proposed. The proposed method works by analyzing the spatial characteristics of the scanned image and utilizing the strong correlation between scanned media type and the spatial characteristics for the corresponding reproduction process. What is needed is an alternative approach for automatic media identification.